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Abstract:

A method for mapping wireless resources of reference symbols for channel
state estimation and modulation symbols for user information transmission
in a transmitter of an Orthogonal Frequency Division Multiplexing (OFDM)
mobile communication system is disclosed. The mapping method includes
channel-encoding and modulating a user information stream to be
transmitted, and then generating a systematic symbol stream and a parity
symbol stream; and preferentially arranging systematic modulation symbols
in resource elements of a symbol including no reference symbol, and then
arranging parity modulation symbols in remaining resource elements.

Claims:

1. A method for mapping wireless resources of reference symbols for
channel state estimation and modulation symbols for user information
transmission in a transmitter of an Orthogonal Frequency Division
Multiplexing (OFDM) mobile communication system, the method
comprising:channel-encoding and modulating a user information stream to
be transmitted;generating a systematic symbol stream containing
systematic modulation symbols and a parity symbol stream containing
parity modulation symbols using the user information stream;
andpreferentially arranging the systematic modulation symbols in resource
elements of a symbol including no reference symbol, and then arranging
the parity modulation symbols in remaining resource elements.

2. The method of claim 1, wherein generating a systematic symbol stream
and a parity symbol stream comprises:dividing channel-coded bits into a
systematic bit stream and a parity bit stream;modulating the systematic
bit stream and the parity bit stream separately, to convert them into a
systematic symbol stream and a parity symbol stream, respectively;
andinterleaving the systematic symbol stream and the parity symbol stream
independently.

3. The method of claim 1, wherein arranging modulation symbols in resource
elements comprises:preferentially and sequentially arranging the
systematic modulation symbols along a frequency domain in one symbol
interval including no reference symbol, and then sequentially arranging
the systematic modulation symbols along the frequency domain in a next
symbol interval including no reference symbol.

4. The method of claim 1, wherein arranging modulation symbols in resource
elements comprises:preferentially and sequentially arranging the
systematic modulation symbols along a time domain in a symbol interval
including no reference symbol in one frequency tone, and then
sequentially arranging the systematic modulation symbols along the time
domain in the symbol interval in a next frequency tone.

5. A method for demapping wireless resources of reference symbols for
channel state estimation and modulation symbols for user information
transmission in a receiver of an Orthogonal Frequency Division
Multiplexing (OFDM) mobile communication system, the method
comprising:detecting, from a received signal, a systematic symbol stream
containing systematic modulation symbols arranged in resource elements of
a symbol including no reference symbol and detecting a parity symbol
stream containing parity modulation symbols arranged in remaining
resource elements;deinterleaving the systematic symbol stream and the
parity symbol stream separately;demodulating the systematic symbol stream
and the parity symbol stream independently, to convert them into a
systematic bit stream and a parity bit stream, respectively; andcombining
the systematic bit stream with the parity bit stream, and decoding the
combined bit stream to generate a user information stream.

6. An apparatus for mapping modulation symbols according to power
allocation for reference symbols in a transmitter of a mobile
communication system, the apparatus comprising:a channel encoder for
converting an input user bit stream into a coded bit stream;a
demultiplexer for demultiplexing the coded bit stream into a systematic
bit stream and a parity bit stream;a first modulator for modulating the
systematic bit stream;a second modulator for modulating the parity bit
stream;a first interleaver for interleaving the systematic bit stream
output from the first modulator;a second interleaver for interleaving the
parity bit stream output from the second modulator; anda resource element
mapper for preferentially arranging the systematic bit stream output from
the first interleaver in resource elements of a symbol including no
reference symbol, and arranging the parity bit stream output from the
second interleaver in remaining resource elements.

7. The apparatus of claim 6, wherein the resource element mapper
preferentially and sequentially arranges systematic modulation symbols
along a frequency domain in one symbol interval including no reference
symbol, and then sequentially arranges systematic modulation symbols
along the frequency domain in a next symbol interval including no
reference symbol.

8. The apparatus of claim 6, wherein the resource element mapper
preferentially and sequentially arranges systematic modulation symbols
along a time domain in a symbol interval including no reference symbol in
one frequency tone, and then sequentially arranges systematic modulation
symbols along the time domain in the symbol interval in a next frequency
tone.

9. An apparatus for demapping modulation symbols according to power
allocation for reference symbols in a receiver of a mobile communication
system, the apparatus comprising:a reception processor for converting a
received radio signal into baseband data;a resource element demapper for
detecting, from among symbols output from the reception processor, a
systematic symbol stream arranged in resource elements of a symbol
including no reference symbol and detecting a parity symbol stream
arranged in remaining resource elements;a first deinterleaver for
deinterleaving the systematic symbol stream;a second deinterleaver for
deinterleaving the parity symbol stream;a first demodulator for
demodulating the systematic symbol stream output from the first
deinterleaver;a second demodulator for demodulating the parity symbol
stream output from the second deinterleaver;a multiplexer for
multiplexing the systematic bit stream and the parity bit stream output
from the first and second demodulators; anda channel decoder for
converting the bit stream output from the multiplexer into a decoded user
bit stream.

Description:

PRIORITY

[0001]This application claims priority under 35 U.S.C. §119(a) to a
Korean Patent Application filed in the Korean Intellectual Property
Office on Apr. 13, 2007 and assigned Serial No. 2007-36669, the
disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present invention relates generally to a communication system
using a multiple access scheme, and in particular, to a method and
apparatus for transmitting and receiving both reference symbols and data
symbols.

[0004]2. Description of the Related Art

[0005]Recently, in mobile communication systems, intensive research is
being conducted on Orthogonal Frequency Division Multiplexing (OFDM) as a
scheme useful for high-speed data transmission in wire/wireless channels.
OFDM, a scheme for transmitting data using multiple carriers, is a type
of Multi-Carrier Modulation (MCM) that converts a serial input symbol
stream into parallel symbol streams and modulates each of them with a
plurality of orthogonal frequency tones, i.e., subcarrier channels,
before transmission.

[0006]The MCM-based system was first applied to military high-frequency
radios in the late 1950s, and the OFDM scheme, which overlaps multiple
orthogonal subcarriers, has been developing since 1970s. But there were
limitations on its application to the actual systems due to the
difficulty in realization of orthogonal modulation between multiple
carriers. However, the OFDM scheme has undergone rapid development since
Weinstein et al. presented in 1971 that OFDM-based
modulation/demodulation can be efficiently processed using DFT (Discrete
Fourier Transform). In addition, as a scheme is known that uses a guard
interval and inserts a Cyclic Prefix (CP) symbol into the guard interval,
the negative influence of the system on the multiple paths and delay
spread has been reduced significantly.

[0007]Owing to such technical developments, the OFDM technology is being
widely applied to the digital transmission technologies such as Digital
Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), Wireless
Local Area Network (WLAN), Wireless Asynchronous Transfer Mode (WATM),
etc. That is, the OFDM scheme could not be widely used before due to its
high hardware complexity, but the development of various digital signal
processing technologies including Fast Fourier Transform (FFT) and
Inverse Fast Fourier Transform (IFFT) has enabled its realization. The
OFDM scheme, though it is similar to the conventional Frequency Division
Multiplexing (FDM) scheme, can obtain optimal transmission efficiency
during high-seed data transmission by maintaining orthogonality between
multiple tones during transmission. In addition, the OFDM scheme can
obtain the optimal transmission efficiency during high-speed data
transmission as it has high frequency utilization efficiency and is
robust against multipath fading. Further, the OFDM scheme, as it overlaps
frequency spectra, has high frequency utilization efficiency, is robust
against frequency selective fading, can reduce an Inter-Symbol
Interference (ISI) effect with the use of a guard interval, can design
simple hardware of an equalizer, and is robust against impulse noises.
Therefore, the OFDM scheme is used for various communication systems.

[0008]In wireless communications, high-speed, high-quality data services
are generally hindered by the channel environments. In wireless
communications, the channel environments suffer from frequent changes not
only due to additive white Gaussian noise (AWGN) but also power variation
of received signals, caused by a fading phenomenon, shadowing, a Doppler
effect brought by movement of a terminal and a frequent change in a
velocity of the terminal, interference by other users or multipath
signals, etc. Therefore, in order to support high-speed, high-quality
data services in wireless communication, there is a need to efficiently
overcome the above factors.

[0009]In OFDM, modulation signals are located in the two-dimensional
time-frequency resources. Resources on the time domain are divided into
different OFDM symbols, and are orthogonal with each other. Resources on
the frequency domain are divided into different tones, and are also
orthogonal with each other. That is, the OFDM scheme defines one minimum
unit resource by designating a particular OFDM symbol on the time domain
and a particular tone on the frequency domain, and the unit resource is
called a "frequency-time bin". Since different frequency-time bins are
orthogonal with each other, signals transmitted with different
frequency-time bins can be received without causing interference to each
other. In terms of resource allocation, the frequency-time bin is also
called a "Resource Element (RE)".

[0010]The mobile communication environment has a characteristic that
channels vary randomly. In order to solve problems caused by the channel
variation, most mobile communication systems are designed to support
coherent demodulation that includes a process of estimating states of
channels and correcting the estimated channel states. In order to
estimate the random states of channels, a signal previously agreed upon
between a transmitter and a receiver is transmitted. Such a signal is
called a "pilot" or "Reference Symbol (RS) signal". The receiver, by
receiving the RS signal, estimates states of channels and corrects the
estimated channel states, thereby performing demodulation. The number of
RS signals transmitted should be large enough to be able to estimate the
change in channels, and it is preferable that they are not damaged by
data signals. In the OFDM system, it is possible to prevent RS signals
from being damaged by data signals by arranging the RS signals in
predetermined frequency-time bins.

[0011]FIG. 1 illustrates an RS pattern when 2 transmit antennas are used,
defined by a Long Term Evolution (LTE) system of the 3rd Generation
Partnership Project (3GPP).

[0012]Referring to FIG. 1, one Resource Block (RB) is composed of 12 tones
on the frequency domain and 14 OFDM symbols on the time domain. Shown in
FIG. 1 is a bandwidth composed of a total of N RBs of RB#1 121 to RB#N
123.

[0013]Of frequency-time bins, bins 131 denoted by "a" are RSs transmitted
via a first antenna, and bins 133 denoted by "b" are RSs transmitted via
a second antenna. If a base station has one transmit antenna, the
frequency-time bins 133 denoted by "b" will be used for data
transmission. Since RS signals are previously agreed upon between a base
station and a terminal, the terminal can estimate channels from the first
transmit antenna based on received signals of the frequency-time bins "a"
131, and estimate channels from the second transmit antenna based on
received signals of the frequency-time bins "b" 133.

[0014]Regarding the characteristics of the RS pattern shown in FIG. 1,
OFDM symbols are divided into symbols including RSs and symbols including
no RS. That is, while RSs are defined in a 1st OFDM symbol 101, a
5th OFDM symbol 103, an 8th OFDM symbol 105 and a 12th
OFDM symbol 107, no RS is defined in the remaining OFDM symbols 111, 113,
115 and 117. Regarding RSs for one transmit antenna, every 6th tone
is inserted, and regarding even RSs for another transmit antenna, every
6th tone is inserted between the RS tones.

[0016]Referring to FIG. 2, RSs 131 for a first transmit antenna and RSs
133 for a second transmit antenna are inserted in the same positions as
those of FIG. 1, and RS 135 for a third transmit antenna and RS 137 for a
fourth transmit antenna are additionally defined. Since the added RSs are
arranged in a 2nd OFDM symbol 201 and a 9th OFDM symbol 203,
OFDM symbols including RSs include 6 OFDM symbols 101, 103, 105, 107, 201
and 203 among a total of 14 OFDM symbols, and the remaining OFDM symbols
211, 213, 215 and 217 include no RS.

[0017]In order to guarantee channel estimation performance of terminals,
there is a need to allocate sufficient power for RSs. In particular, when
data is transmitted to a terminal having a poor channel state, a required
Signal to Noise Ratio (SNR) is secured with use of a method such as
Automatic Repeat reQuest (ARQ). However, for RSs, it is not possible to
improve their SNR through ARQ, so there is a need to sufficiently secure
power of RSs. Therefore, power of RSs is first allocated and the
remaining power is used for data transmission. In this case, when
sufficient power is allocated for RSs, available power per tone for data
transmission in OFDM symbols including RSs may be lower than that in OFDM
symbols including no RS.

[0018]FIG. 3 illustrates power allocation for data tones according to RS
power allocation when there is one transmit antenna.

[0019]Referring to FIG. 3, reference numeral 301 represents tones defined
in one RB in OFDM symbols including RSs, and reference numeral 303
represents tones in OFDM symbols including no RS. Reference numeral 301
represents RB of OFDM symbols 101 and 105 of FIG. 1, and the RB 301 is
composed of RS tones 311 and data tones 313. The RB 303 is composed of
only data tones 315. Power P is allocated to RS tones, and its value is
set higher than power D of data tones in OFDM symbols including no RS. A
condition that a sum of power allocated to one RB is equal for each OFDM
symbol can be expressed as Equation (1).

NRS×P+(N-NRS)×D*=N×D (1)

[0020]In Equation (1), N denotes the number of tones constituting one RB,
and N=12 in the example of FIG. 3; NRS denotes the number of RS tones
defined in one RB in an OFDM symbol including RSs, and NRS=2 in the
example of FIG. 3; and D* denotes power of data tones in an OFDM symbol
including RSs.

[0021]If P>D, since N>NRS, D*<D as shown in Equation (2).

P-D=(N/NRS-1)×(D-D*)>0 (2)

[0022]That is, power of data tones in an OFDM symbol including RSs must be
set lower than power of data tones in an OFDM symbol having no RS.

[0023]FIG. 4 illustrates a general channel coding process. When a user's
information bit stream 401 is input to a channel encoder 403, a coded bit
stream 405 is output. The coded bit stream 405 can be divided into a
systematic bit stream 411 which is the same bit stream as the user's
information bit stream 401 being input to the channel encoder 403, and a
parity bit stream 413 whose decoding performance is improved. If a
receiver has failed in successfully restoring the user's information bit
stream 401 by first receiving the systematic bit stream 411, it attempts
decoding referring to both the parity bit stream 413 and the systematic
bit stream 411. That is, if the receiver has successfully restored the
transmission signal only with the systematic bit stream, it has no need
to perform an additional decoding process. In terms of the decoding
performance, the systematic bit stream is more important than the parity
bit stream. When the systematic bit stream and the parity bit stream are
damaged in the same ratio, the damaged systematic bit stream causes a
greater reduction in the final decoding performance, compared to the
damaged parity bit stream. Therefore, the use of a method capable of
protecting the systematic bit stream if possible, shows higher
performance compared to the use of a method for protecting the parity bit
stream.

SUMMARY OF THE INVENTION

[0024]An aspect of the present invention is to address at least the
problems and/or disadvantages above and to provide at least the
advantages described below. Accordingly, an aspect of the present
invention is to provide a method and apparatus for mapping modulation
symbols to Resource Elements (REs) taking arrangement of RSs into account
so that a systematic bit stream may be better protected than a parity bit
stream.

[0025]Another aspect of the present invention is to provide a method and
apparatus capable of improving decoding performance in the same channel
environment.

[0026]According to one aspect of the present invention, there is provided
a method for mapping wireless resources of reference symbols for channel
state estimation and modulation symbols for user information transmission
in a transmitter of an Orthogonal Frequency Division Multiplexing (OFDM)
mobile communication system. The mapping method includes channel-encoding
and modulating a user information stream to be transmitted; generating a
systematic symbol stream containing systematic modulation symbols and a
parity symbol stream containing parity modulation symbols using the user
information stream; and preferentially arranging the systematic
modulation symbols in resource elements of a symbol including no
reference symbol, and then arranging the parity modulation symbols in
remaining resource elements.

[0027]According to another aspect of the present invention, there is
provided a method for demapping wireless resources of reference symbols
for channel state estimation and modulation symbols for user information
transmission in a receiver of an Orthogonal Frequency Division
Multiplexing (OFDM) mobile communication system. The demapping method
includes detecting, from a received signal, a systematic symbol stream
containing systematic modulation symbols arranged in resource elements of
a symbol including no reference symbol and detecting a parity symbol
stream containing parity modulation symbols arranged in remaining
resource elements; deinterleaving the systematic symbol stream and the
parity symbol stream separately; demodulating the systematic symbol
stream and the parity symbol stream independently, to convert them into a
systematic bit stream and a parity bit stream, respectively; and
combining the systematic bit stream with the parity bit stream, and
decoding the combined bit stream to generate a user information stream.

[0028]According to further another aspect of the present invention, there
is provided an apparatus for mapping modulation symbols according to
power allocation for reference symbols in a transmitter of a mobile
communication system. The mapping apparatus includes a channel encoder
for converting an input user bit stream into a coded bit stream; a
demultiplexer for demultiplexing the coded bit stream into a systematic
bit stream and a parity bit stream; a first modulator for modulating the
systematic bit stream; a second modulator for modulating the parity bit
stream; a first interleaver for interleaving the systematic bit stream
output from the first modulator; a second interleaver for interleaving
the parity bit stream output from the second modulator; and a resource
element mapper for preferentially arranging the systematic bit stream
output from the first interleaver in resource elements of a symbol
including no reference symbol, and arranging the parity bit stream output
from the second interleaver in remaining resource elements.

[0029]According to yet another aspect of the present invention, there is
provided an apparatus for demapping modulation symbols according to power
allocation for reference symbols in a receiver of a mobile communication
system. The demapping apparatus includes a reception processor for
converting a received radio signal into baseband data; a resource element
demapper for detecting, from among symbols output from the reception
processor, a systematic symbol stream arranged in resource elements of a
symbol including no reference symbol and detecting a parity symbol stream
arranged in remaining resource elements; a first deinterleaver for
deinterleaving the systematic symbol stream; a second deinterleaver for
deinterleaving the parity symbol stream; a first demodulator for
demodulating the systematic symbol stream output from the first
deinterleaver; a second demodulator for demodulating the parity symbol
stream output from the second deinterleaver; a multiplexer for
multiplexing the systematic bit stream and the parity bit stream output
from the first and second demodulators; and a channel decoder for
converting the bit stream output from the multiplexer into a decoded user
bit stream.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]The above and other aspects, features and advantages of the present
invention will become more apparent from the following detailed
description when taken in conjunction with the accompanying drawings in
which:

[0031]FIG. 1 is a diagram illustrating an RS pattern when 2 transmit
antennas are used, according to the prior art;

[0032]FIG. 2 is a diagram illustrating an RS pattern when 4 transmit
antennas are used, according to the prior art;

[0033]FIG. 3 is a diagram illustrating power allocation for data tones
based on RS power allocation according to the prior art;

[0034]FIG. 4 is a diagram illustrating a general channel coding process;

[0035]FIG. 5 is a diagram illustrating a modulation process of converting
a systematic bit stream and a parity bit stream into a systematic
modulation symbol stream and a parity modulation symbol stream through
modulation, respectively, according to an embodiment of the present
invention;

[0036]FIG. 6 is a diagram for a description of symbol mapping according to
an embodiment of the present invention;

[0037]FIG. 7 is a signal flow diagram illustrating an operation of a
transmitter according to an embodiment of the present invention;

[0038]FIG. 8 is a diagram illustrating a structure of a base station's
transmitter according to an embodiment of the present invention; and

[0039]FIG. 9 is a diagram illustrating a structure of a terminal's
receiver according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040]Preferred embodiments of the present invention will now be described
in detail with reference to the annexed drawings. The matters defined in
the description such as a detailed construction and elements are provided
to assist in a comprehensive understanding of the preferred embodiments
of the invention. Accordingly, those of ordinary skill in the art will
recognize that various changes and modifications of the embodiment
described herein can be made without departing from the scope and spirit
of the invention. Also, descriptions of well-known functions and
constructions are omitted for clarity and conciseness.

[0041]The present invention provides a technology for mapping modulation
symbols to REs so that parts corresponding to a systematic bit stream in
a coded bit stream should not be allocated to REs of an OFDM symbol
including RSs, when power allocated to REs of the OFDM symbol including
RSs is set lower than power allocated to REs of an OFDM symbol including
no RS due to the power allocation for RSs, thereby improving decoding
performance. To this end, it is necessary to divide modulation symbols
into systematic modulation symbols generated only with systematic bits
and parity modulation symbols generated only with parity bits, and
process the modulation symbols so that the systematic modulation symbols
may not be allocated to REs of an OFDM symbol including RSs.

[0043]Modulators 521A and 521B perform the same modulation scheme. The
modulation scheme is determined based on a downlink Channel Quality
Indicator (CQI) being fed back from a terminal to a base station and a
status of a transmission buffer in the base station, etc. Although the
modulation scheme is subject to change according to the above conditions,
the modulation scheme applied to the systematic bit stream is equal to
the modulation scheme applied to the parity bit stream.

[0044]FIG. 6 is a diagram for a description of symbol mapping for REs. REs
501 where RSs will be arranged are arranged as described in FIGS. 1 and
2. In an example of FIG. 6, since one transmit antenna is considered,
only RSs for a first transmit antenna are defined. REs where RSs for
other transmit antennas are scheduled to be arranged are used for
transmitting data symbols. REs where data symbols will be arranged are
divided into two types. First type REs 503 for data symbols (hereinafter
"first-type data symbol REs 503") are REs for data transmission, defined
in OFDM symbols 101, 103, 105 and 107 including RSs, and second type REs
for data symbols (hereinafter "second-type data symbol REs 505") are REs
for data transmission, defined in OFDM symbols 111, 113, 115 and 117
including no RS. As stated in Equation (2), the first-type data symbol
REs 503 are allocated lower power than the second-type data symbol REs
505 due to the need for sufficient power allocation for RSs.

[0045]The present invention defines a method for mapping modulation
symbols to REs so that a systematic modulation symbol stream composed of
a systematic bit stream should not be arranged in the first-type data
symbol RE s 503. A parity modulation symbol stream composed of a parity
bit stream can be arranged in either the first-type data symbol REs 503
or the second-type data symbol REs 505.

[0046]The reason for this mapping scheme is because a system protecting
systematic bits shows higher performance than a system protecting parity
bits. Since lower power is allocated to the first-type data symbol REs
503 and higher power is allocated to the second-type data symbol REs 505,
it is preferable that the systematic modulation symbols are arranged in
the in the second-type data symbol REs 505.

[0047]When a channel coding rate is low, due to the low ratio of
systematic bits, there may be remaining second-type data symbol REs even
after all the systematic bits are arranged in the second-type data symbol
REs. In this case, parity modulation symbols are arranged in the
first-type data symbol REs and the remaining second-type data symbol REs.

[0048]When the channel coding rate is high, due to the high ratio of
systematic bits, there may be remaining systematic modulation symbols
even after the systematic bits are arrange in the second-type data symbol
REs. In this case, the parity modulation symbols and the remaining
systematic modulation symbols are arranged in the first-type data symbol
REs.

[0049]In sum, modulation symbols are arranged so that the systematic
modulation symbols are first arranged in REs of OFDM symbols including no
RS.

[0050]Example of Mapping Rule

[0051]A description will now be made of an example of realizing a mapping
rule proposed by the present invention. In this example, a systematic
modulation symbol stream and a parity symbol stream are separately
interleaved. The interleaving is an operation of permuting symbol streams
so that consecutive bit errors (burst error) should not occur in the
channel-coded bit stream. If systematic parts and parity parts undergo
interleaving independently, the systematic modulation symbol stream and
the parity modulation symbol stream are not mixed. The two symbol streams
are concatenated such that the systematic modulation symbol stream is
followed by the parity modulation symbol stream. As a result, the
modulation symbols located in the front are systematic modulation
symbols, and the modulation symbols located in the rear are parity
modulation symbols. The symbol streams concatenated in this way are
mapped to the REs in the following order.

[0052]FIG. 6 is a diagram for a description of symbol mapping according to
an embodiment of the present invention.

[0053]A concatenated symbol stream is sequentially arranged in REs defined
in 3 OFDM symbols 111 of FIG. 6 in such a manner that frequency tones are
first filled sequentially, and after frequency tones of one RB are fully
filled up, REs of the next OFDM symbol are filled. When all REs of the
OFDM symbols 111 are fully filled up, REs of the OFDM symbols are filled
with the remaining symbol stream in the order of OFDM symbols 113, 115
and 117, and thereafter, in the order of OFDM symbols 101, 103, 105 and
107. Since the use of the above mapping method locates the systematic
modulation symbols in the front, the second-type data symbol REs are
filled first with the systematic modulation symbols.

[0054]An alternative embodiment can first sequentially insert modulation
symbols along the time domain in the intervals 111, 113, 115 and 117
including no RS, which are intervals where OFDM symbols are filled, and
then sequentially fill the intervals with the modulation symbols after
going to the next frequency tones.

[0055]FIG. 7 is a signal flow diagram illustrating an operation of a
transmitter according to an embodiment of the present invention.

[0056]In step 710, the transmitter channel-encodes a user information
stream. In step 720, the transmitter divides the channel-coded bits into
a systematic bit stream and a parity bit stream. In step 730, the
transmitter converts the systematic bit stream and the parity bit stream
into a systematic modulation symbol stream and a parity modulation symbol
stream through modulation separately. In step 740, the transmitter
interleaves the systematic modulation symbol stream and the parity
modulation symbol stream independently. Thereafter, in step 750, the
transmitter arranges modulation symbols so that the systematic modulation
symbols are first arranged in REs of OFDM symbols including no RS.
Finally, in step 760, the transmitter performs transmission processing
processes such as a process of multiplexing the modulation symbols with
another user's data channel, control channel, RS signal, etc., an IFFT
and CP attachment process for completing an OFDM signal, and a Radio
Frequency (RF) processing process.

[0057]A receiver should rearrange a received modulation symbol stream
according to the mapping rule considered in step 750, and deinterleave
the systematic modulation symbols and the parity modulation symbols
separately. Since such a demapping method in the receiver is a reverse
process of the symbol mapping method of a mapper in the transmitter, a
detailed description thereof will be omitted herein.

[0058]FIG. 8 is a diagram illustrating a structure of a base station's
transmitter according to an embodiment of the present invention.

[0059]A user bit stream is input to a channel encoder 801 where it is
converted into a coded bit stream. In a demultiplexer 803, the coded bit
stream is divided into a systematic bit stream and a parity bit stream,
and the systematic bit stream and the parity bit stream undergo separate
modulations 805A and 805B and interleavings 807A and 807B, respectively.
Reference numerals 805A and 807A represent a modulator and an interleaver
for the systematic bit stream and the systematic symbol stream, and
reference numerals 805B and 807B represent a modulator and an interleaver
for the parity bit stream and the parity symbol stream. As provided by
the present invention, the systematic symbol stream is first arranged in
REs of OFDM symbols including no RS by means of an RE mapper 809. The
symbol stream output from the RE mapper 809 is transmitted after
undergoing, in a transmission processor 811, a transmission processing
process such as multiplexing with other channels, IFFT, CP attachment, RF
processing, etc.

[0060]FIG. 9 is a diagram illustrating a structure of a terminal's
receiver according to an embodiment of the present invention.

[0061]Regarding a received signal, a reception processor 951 receives a
signal of an RB that the user is allocated, through a reception
processing process such as RF processing, CP detachment, FFT,
demultiplexing with other channels, channel estimation, etc. An RE
demapper 953 rearranges in reverse the received modulation symbol stream
according to the arrangement rule of the modulation symbols, used by the
RE mapper 809 in FIG. 8 of the transmitter. The systematic parts in the
received symbol stream undergo deinterleaving in a deinterleaver 955A and
demodulation in a demodulator 957A, thereby being restored as a
systematic bit stream, and the parity parts undergo deinterleaving in a
deinterleaver 955B and demodulation in a demodulator 957B, thereby being
restored as a parity bit stream. The restored systematic bit stream and
parity bit stream are united into one received bit stream by means of a
multiplexer 961, and restored to a decoded bit stream by means of a
channel decoder 963.

[0062]As is apparent from the foregoing description, the present invention
provides for arranging modulation symbols so that the systematic
modulation symbols should be first arranged in REs of OFDM symbols
including no RS. Since REs of OFDM symbols including RSs (i.e., the
first-type data symbol REs) are allocated lower power than REs of OFDM
symbols including no RS (i.e., the second-type data symbol REs), when
systematic modulation symbols are arranged in the REs of OFDM symbol
including no RS if possible, the systematic modulation symbols are first
allocated more power compared to the parity modulation symbols. In the
same condition, since protecting the systematic bits improves the
decoding performance compared to protecting the parity bits, application
of the arrangement rule proposed by the present invention can contribute
to a decrease in an error rate.

[0063]While the invention has been shown and described with reference to
certain preferred embodiments thereof, it will be understood by those
skilled in the art that various changes in form and details may be made
therein without departing from the spirit and scope of the invention as
defined by the appended claims.